iMac freezes complete, except mouse pointer. What can I do?

Question

Recently, I've noticed a strange behavior on my iMac (Yosemite 10.10.4, Late 2009).

Everything freezes completely - it's totally unresponsive. HOWEVER, I can continue to control the mouse pointer perfectly.

In other words - even though I can move the pointer - I can't click any buttons, menu items, change the focus on any windows, or interact with the desktop, dock, menu, or any running app. Launchpad and Mission Control don't work. The iMac also doesn't seem to respond to the keyboard at all.

I should note that this happens very infrequently - perhaps once or twice a month. I haven't noticed a pattern of when it happens (e.g., it doesn't typically happen soon after restarting).

So...

1. Any idea what might cause this? I'm up to date on all my updates (OS X and apps), and I'm not doing anything out of the ordinary with my Mac (No envelope-pushing applications or modifications).
2. So far - the only thing I can think of to fix this is hold down the power button until it restarts. Is there a better option? (E.g., on Windows, you have CTRL+ALT+DELETE, which seems to recover from any crash short of a full blue-screen). Is there an equivalent way to launch the activity monitor, for example?

Answer 1

I had this problem as well, it turns out that migrating from a prior version was the problem, specifically kernel extensions that used to worked now "sorta" worked until they didn't.

Using Lingon (see the Apple Store), it was possible turn on and off various services to locate the problematic one(s). Using Onyx it was possible to clear out the kernel caches.

For me it was some historic SnapZPro extensions that needed updating.

Answer 2

My imac did the same thing, but I assumed that it might have something to do with the fans. so I opened it up, and used an air hose from my compressor to clean the fans... they were completely covered in dust. This was causing them to run slow and not run at all. after this I put the imac back together... good as new. BTW I watched a YouTube video that was very helpful to help me remove the screen. it is just held on by magnets, then you take off 8 screws, and remove lcd... blow it out, the assemble.

Answer 3

This has happened to me a few times over the years and I discovered by accident that my wireless mouse was accidently on and depressed, in my computer bag. So sometimes it is so simple!! My problem is I always tend to forget and then after scratching my head for a while I remember about the mouse. I hope your fix is as simple as mine.

Answer 4

What you don't say is how long your Mac works before exhibiting this behavior. That might help.

What I would do is boot into safe mode (hold Shift at startup until you see the Apple logo) And see if the system still freezes up. If it does then it is likely that something you have installed is causing the freeze up. The fun part is then turning off startup items one or two at a time and booting normally till you find the culprit..

if it is the same in safe mode then the OS is likely damaged or you have a hardware failure of some sort. At that point I would back up your drive, wipe it and install the OS fresh. When you restore your stuff only restore documents (not applications) and start with only the ones you absolutely have to have and run the system for a bit between installs until the symptoms recur.